Before you blame the HV battery in your hybrid vehicle, check out the 12 volt battery.
1) The dashboard lights up, the gear shift box shows, but when you turn the ignition key nothing happens. Sometimes you will see the dash dim and nothing happens.
2) The car starts but idiot light such as power steering etc shows but they still work and the vehicle seems to be working eratically.
Unlike normal petrol vehicles the 12 volt battery in the Toyota Prius Hybrid is not used to start the petrol engine. The problem here is that the 12 volt battery does not have enough charge to power the computers. Check the voltage of the 12 volt battery. It should be at least 12.5 volts.
If the battery is weak change it and presto - you are away again. This advise will probably save you some money as the local mechanic who may not know too much could charge you many hours to discover this problem or to not discover this problem!